Since the discovery of norfloxacin, attempts have been made to improve the antimicrobial activity and pharmacokinetics of synthetic quinolone antimicrobial agents. As a result, a number of compounds are clinically available today as chemotherapeutic drugs efficacious in treating systemic infectious diseases.
In recent years, however, bacteria hyposensitive to these drugs have been increasing in the field of clinical medicine. Moreover, some bacteria tolerant to drugs other than these synthetic quinolone antimicrobial agents have also become hyposensitive thereto. Staphylococcus aureus (MRSA) is an example of such bacteria having no sensitivity to .beta.-lactam antibiotics. Therefore, there is an urgent need to develop highly efficacious drugs in the field of clinical medicine.
In addition, it is reported that these antimicrobial agents sometimes induce convulsions when administered together with nonsteroidal anti-inflammatory drugs and exhibit other side effects such as phototoxicity. Thus, there is also a need to develop safer quinolone drugs.